Implantable medical devices providing diagnostics and/or therapy delivery are often fixed to an implant site within a body of a patient by a helical element. FIGS. 1A-B are plan views of portions of exemplary medical devices, each of which include such an element for fixation; and FIG. 2 is a schematic depicting potential implant sites for the devices. FIGS. 1A and 2 illustrate a first of the exemplary medical devices including an elongate body 100 and a helix fixation element 150 coupled thereto and terminating a distal end thereof. FIGS. 1A-2 further illustrate an electrode 130 mounted around body 100 and offset proximally from helix fixation element 150. FIGS. 1B and 2 illustrate a second exemplary medical device 200 including an elongate body 10 to which a helix fixation element 15 is coupled such that element 15 extends around body 10. FIGS. 1B and 2 further illustrate an electrode 17 terminating a distal end of body 10, being offset distally from helix fixation element 15. With reference to FIGS. 1A-B, each helix fixation element 150, 15 includes a piercing tip T-150, T-15 for engaging tissue at the implant site. FIG. 2 shows device 200 also including a pulse generator 20, such as is known to those skilled in the art, which is located in a pectoral region of the patient, and to which elongate body 10 is coupled. Although not shown, body 100 may be coupled to a similar pulse generator which is located in another region of the patient, for example, abdominal. Either of helix fixation elements 150, 15 may also function as an electrode, for example, for bipolar pacing and sensing in conjunction with the corresponding electrode 130, 17. Alternately, each medical device need not include the corresponding electrode 130, 17, and helix fixation element 150, 15 may or may not function as an electrode.
With further reference to FIG. 2, elongate body 10 is implanted trans-venous, at an epicardial site within a cardiac vein CV, and elongate body 100 is implanted trans-thoracic, also at an epicardial site, but outside any of the cardiac blood vessels. FIGS. 3A-B are cross-section schematics of the exemplary devices of FIGS. 1A-B implanted at each site. FIG. 3A illustrates body 10 located within cardiac vein CV, and piercing tip T-15 of helix fixation element 15 engaging tissue of the myocardium M. FIG. 3B illustrates body 100 located between the myocardium M and pericardial sac PS, and piercing tip T-150 engaging tissue of the myocardium M. In each exemplary case, initial engagement of fixation element 15, 150 with myocardium M, as opposed to within an opposing wall of cardiac vein CV or pericardial sac PS, is preferred for more stable fixation. Furthermore, if helix fixation element 15, 150 also functions as an electrode for cardiac pacing, engagement thereof with the myocardium M may be important for adequate pacing thresholds. Those skilled in the art appreciate the difficulties deploying body 10, 100 with piercing tip T-15, T-150 oriented for the illustrated engagement, thus various systems including delivery tools that are directed toward facilitating such a deployment are known in the art. Yet there is still a need for new systems and delivery tools thereof that facilitate deployment of medical diagnostics and/or therapy with helix fixation members of implantable medical devices oriented for the preferred initial engagement piercing tips thereof with tissue at desired implant sites.